The present invention relates to printers and, more specifically, to registration of multiple printheads and/or multiple firing chambers in a printer.
Many types of printers are known and they include ink jet, laser and various thermal and impact printers. Ink jet printers include those that are thermally actuated (e.g., resistive element) and those that are mechanically actuated (e.g., piezo-electric element). Representative ink jet printers include those made by Hewlett Packard, Canon and Epson, etc. The multiple printhead and/or multiple firing chamber registration techniques of the present invention are applicable to all printers and particularly to ink jet printers.
The present invention is directed towards the registration of printing devices within a printer. This registration may be manifested in many ways. A few of these ways are now presented for pedagogical purposes. Multiple printheads or printheads with multiple firing chambers are utilized as a way of delivering color printing (one primary or equivalent color per printhead) and of increasing printing speed and coverage area, amongst other features.
In a thermally actuated multiple printhead printer, the ink expulsion elements are usually formed as resistors in a semiconductor substrate. Due to variations in the semiconductor fabrication process, the size of these resistors may vary between wafers and even between dies from the same wafer. Since different size resistors have different power draws, the same firing current delivered to two different resistors will produce different magnitude thermal pulses and hence different sized ink drops. The different sized ink drops in turn result in printed images that are more strongly of one color than another, for example.
Another relevant registration consideration arises when multiple printheads (or multiple firing chambers in a single printhead) are used in a printing apparatus that prints on a curved surface, e.g., a plotter or other printer with a roll bar. A flat printing device surface used in conjunction with a curved printing surface will normally result in some of the printheads or firing chambers being situated closer to the print media than others. Since it will take longer for ink from the more distant printheads or chambers to arrive at the print media, ink drops will not align appropriately, thus resulting in reduced image quality.
A need thus exists to provide registration in multiple printhead or firing chamber printers so that similarly sized ink drops are delivered in a timely manner to print media.
Accordingly, it is an object of the present invention to provide a printing apparatus that provides registration of printhead and/or firing chambers to achieve improved image quality.
It is another object of the present invention to provide a printing apparatus that increases the uniformity of the size of ink drops delivered to print media.
It is also an object of the present invention to achieve such registration and related benefits by modifying the timing and/or strength of firing signals delivered to ink expulsion elements.
These and related object of the present invention are achieved by use of a printhead registration apparatus and method as described herein.
The attainment of the foregoing and related advantages and features of the invention should be more readily apparent to those skilled in the art, after review of the following more detailed description of the invention taken together with the drawings.